Hard disk-type magnetic media are widely utilized in various applications, particularly in the computer industry. A conventional longitudinal recording, hard magnetic disk-type medium 1 commonly employed in computer-related applications is schematically depicted in FIG. 1, and comprises a substantially rigid, non-magnetic metal substrate 10, typically of an aluminum (Al) alloy, such as an aluminum-magnesium (Al-Mg) alloy, having sequentially deposited thereon a plating layer 11, such as of amorphous nickel-phosphorus (Ni-P), a polycrystalline seed or underlayer 12, typically of chromium (Cr) or a Cr-based alloy, a magnetic layer 13, e.g., of a cobalt (Co)-based alloy, a protective overcoat layer 14, typically containing carbon (C), e.g., diamond-like carbon (“DLC”) formed, as is known, by sputtering of a carbon target in an appropriate atmosphere or by ion beam deposition (“IBD”) utilizing appropriate precursor gases, and a lubricant topcoat layer 15, typically of a perfluoropolyether compound applied, as is known, by dipping, spraying, etc. The magnetic layer 13 typically comprised of a Co-based alloy may be formed by sputtering techniques and includes polycrystallites epitaxially grown on the polycrystalline Cr or Cr-based alloy underlayer 12.
In operation of medium 1, the magnetic layer 13 can be locally magnetized by a write transducer, or write “head”, to record and thereby store information therein. The write transducer or head creates a highly concentrated magnetic field which alternates direction based on the bits of information to be stored. When the local magnetic field produced by the write transducer is greater than the coercivity of the material of the recording medium layer 13, the grains of the polycrystalline material at that location are magnetized. The grains retain their magnetization after the magnetic field applied thereto by the write transducer is removed. The direction of the magnetization matches the direction of the applied magnetic field. The magnetization of the recording medium layer 13 can subsequently produce an electrical response in a read transducer, or read “head”, allowing the stored information to be read.
Thin film magnetic recording media are conventionally employed in hard disk form for use with disk drives for storing large amounts of data in magnetizable form. Typically, one or more disks are rotated about a central axis in combination with data transducer heads. In operation, a typical contact start/stop (“CSS”) method commences when the transducer head, carried by an air-bearing slider, begins to slide against the surface of the disk as the disk begins to rotate. Upon reaching a predetermined high rotational speed, the head floats in air at a predetermined distance from the surface of the disk due to dynamic pressure effects caused by the air flow generated between the sliding surface of the head and the disk. During reading and recording operations, the transducer head is maintained at a controlled distance from the recording surface, supported on a bearing of air as the disk rotates, such that the head can be freely moved in both the circumferential and radial directions, allowing data to be recorded on and retrieved from the disk at a desired position. Upon terminating operation of the disk drive, the rotational speed of the disk decreases and the head again begins to slide against the surface of the disk and eventually stops in contact with and pressing against the surface of the disk. Thus, the transducer head contacts the disk surface whenever the disk is stationary, accelerated from the static position, and during deceleration just prior to completely stopping. Each time the head and disk assembly is driven, the sliding surface of the head repeats the cyclic sequence consisting of stopping, sliding against the surface of the disk, floating in air, sliding against the surface of the disk, and stopping.
The air bearing design for the head slider/transducer utilized for CSS-type operation as described above provides an interface between the slider and the disk which prevents damage to the disk over the life of the disk/slider/transducer head system, and provides damping in the event the disk drive system undergoes mechanical shock due to vibrations of external origin. The air bearing also provides the desired spacing between the transducer and the disk surface. A bias force is applied to the slider by a flexure armature in a direction toward the disk surface. This bias force is counter-acted by lifting forces from the air bearing until an equilibrium state is achieved. The slider will contact the disk surface if the rotating speed of the disk is insufficient to cause the slider to “fly”, as during start-up and shut-down phases of the CSS cycle. If the slider contacts a data region of the disk, the data may be lost and the disk permanently damaged.
Referring now to FIG. 2, shown therein in perspective view, is a conventionally configured magnetic hard disk 30 having a CSS (i.e., “landing”) zone 36 and a data (i.e., recording) zone 40. More specifically, FIG. 2 illustrates an annularly-shaped magnetic hard disk 30 including an inner diameter 32 and an outer diameter 34. Adjacent to the inner diameter is an annularly-shaped, inner CSS or “landing” zone 36. When disk 30 is operated in conjunction with a magnetic transducer head (not shown in the drawing), the CSS or “landing” zone 36 is the region where the head makes contact with the disk surface during the above-described start-stop cycles or other intermittent occurrences. In FIG. 2, the radially outer edge of the CSS or “landing” zone 36 is indicated by line 38, which is the boundary between CSS zone 36 and data zone 40 where information in magnetic form is stored within the magnetic recording medium layer of disk 30.
It is generally considered desirable for reliably and predictably performing reading and recording operations, and essential for obtaining high areal density magnetic recording, that the transducer head be maintained as close to the disk surface as possible in order to minimize its flying height. Thus, a smooth disk surface is preferred, as well as a smooth opposing surface of the transducer head, thereby permitting the head and the disk to be positioned in very close proximity, with an attendant increase in predictability and consistent behavior of the air bearing supporting the transducer head during motion. However, if the head surface and the recording surface are too flat, the precision match of these surfaces gives rise to friction and “stiction”, i.e., a combination of friction and “stickiness” (resulting from viscous shear forces) at the disk surface which causes the transducer head to adhere to the surface, particularly after periods of non-use, thereby making it more difficult for the transducer head to initiate movement therefrom. Excessive stiction and friction during the start-up and stopping phases of the above-described cyclic sequence causes wear of the transducer and disk surfaces, eventually leading to what is referred to as “head crash”. Another drawback associated with smooth disk surfaces is lack of durability resulting from the very small amount of lubricant which is retained thereon. Thus, there are competing goals of minimizing transducer head flying height (as by the use of smooth surfaces) and reducing transducer head/disk friction (as by avoiding use of smooth surfaces).
Conventional practices for addressing these apparent competing objectives include providing at least the CSS or “landing” zone of the magnetic disk recording medium with a roughened surface to reduce transducer head/disk friction and stiction by a number of different techniques generally known as “texturing”, such as disclosed in U.S. Pat. Nos. 5,626,941; 5,635,269; 5,714,207; 5,718,811; 5,768,076; 5,798,164; 5,945,197; and 6,020,045, the entire disclosures of which are incorporated herein by reference. Referring again to FIG. 1, suitable texturing techniques include, inter alia, circumferential polishing and localized laser heating of the surface of the disk substrate 10 (e.g., of Al—Mg alloy) to create thereon a texture pattern comprising a plurality of spaced apart projections (“bumps”) prior to deposition thereon of a layer stack comprised of plating layer 12, polycrystalline seed or underlayer 12, magnetic layer 13, protective overcoat 14, and lubricant topcoat 15, wherein the textured surface of the underlying disk substrate 10 is substantially replicated in the subsequently deposited, overlying layers. According to such methodology, by providing a textured surface in at least the CSS or “landing” zone, the transducer head is able to rest and slide on the peaks of the projections or “bumps” during starting and stopping, thereby reducing the area of contact between the transducer head and the magnetic medium. As a consequence of the reduced area of contact in the CSS or “landing” zone, the amount of force necessary to initiate movement of the transducer head is considerably reduced. An additional advantage provided by the textured disk surface is the ability to retain a greater amount of lubricant, thereby further increasing disk durability by reducing friction and stiction.
A variety of possible configurations of the textured surface approach for reducing stiction and friction between the transducer head and the disk surface are possible, including texturing only the CSS or “landing” zone, wherein specular smoothness of the data zone is retained for permitting high bit density recording by allowing for very low head flying height; texturing the entire disk surface, i.e., the CSS and data zones, whereby friction and stiction reduction is provided in the data zone in addition to the CSS zone; and separately (i.e., differently) textured CSS and data zones, with and without a transition zone between the differently textured zones, wherein the texturing is optimized for each type of zone to maximize both recording characteristics and mechanical durability.
As previously indicated, in magnetic data/information recording, storage, and retrieval technology, it is continually desired to improve the areal density at which data/information can be recorded and reliably read. Because the recording density of a hard disk and its associated drive mechanism is limited by the distance between the transducer head and the surface of the magnetic medium, a goal of air bearing slider design for use in CSS operation, as described above, is to “fly” the slider as closely as possible to the medium surface while avoiding physical contact or impact with the medium. Smaller spacings, or “fly heights”, are desired so that the transducer head can distinguish between the various magnetic fields emanating from closely spaced regions on the data zone of the disk surface.
The design of the CSS, or landing zone, of advanced, high areal recording density magnetic hard disk media for use with sliders operating at very low flying heights, i.e., 0.7 μinch or less, poses a challenge because the conventional laser zone texturing (“LZT”) technique appropriate for non-padded head sliders is fast approaching its technical limit in that further reduction in bump height to below about 130 Å, e.g., in order to provide lower flying heights of about 0.5 μinch, will inevitably incur stiction failures due to onset of stiction “avalanche”. Stated somewhat differently, stiction cannot be adequately controlled (i.e., moderated) for transducer head sliders operating at such low flying heights, unless relatively tall laser bumps, i.e., greater than about 130 Å, are employed. However, use of such tall bumps entails an increased likelihood of head-disk interference which can result in catastrophic head-disk failures, such as crashes.
A recent development in magnetic hard disk technology (see, for example, U.S. Pat. Nos. 5,418,667 and 5,796,551, and commonly assigned U.S. patent application Ser. No. 09/473,941, filed on Dec. 29, 1999, the entire disclosures of which are incorporated herein by reference) is formation of padded head sliders on the air bearing surface. Padded heads of this type include a plurality of slider pads coated with a wear-resistant material, such as DLC carbon, which face the disk surface during use. As illustrated in the schematic plan view of FIG. 3 showing the lower surface of slider 110, four, small, column-shaped landing pads 118 may be placed on the rails 120 of the flying head slider, proximate the corners thereof, to control stiction. The size and height of the pads 118 are selected such that the pads effectively reduce stiction during takeoff, yet provide sufficient clearance to prevent interference between the head and the disk during normal flying. For example, the total contact area of the four landing pads may be about 0.002-0.003 mm2, and they may be about 300 Å high for providing stiction of about 2-3 gm. In contrast with the behavior exhibited with laser zone textured (“LZT”) media, increased lubricant thickness when padded head sliders are utilized results in a controlled, i.e., linear, increase in stiction.
The DLC-coated slider pads are adapted to contact one or more of the DLC overcoat/lubricant topcoat-coated projections or bumps of the CSS or landing zone of the disk. The combination of DLC-coated slider pads and CSS bumps thus may offer the possibility of reducing stiction and friction during head slider takeoff and landing phases during operation of the disk drive and, as a consequence, provide an improvement in tribological performance.
The pad material of such padded head sliders is not limited to diamond-like carbon (“DLC”), but may, in some applications, comprise the same material as the contact, i.e., lower, surface of the slider, e.g., AlTiC. In addition, depressions or recesses may be formed in the rail surfaces to increase hydrodynamic lift and the number of pads is not restricted, as above, to four pads positioned adjacent the rail corners. For example, a large plurality of micro-pads may be formed extending along the length of the rails. The use of numerous micro-pads is advantageous in that improved reliability is provided, i.e., a single defective pad cannot cause a catastrophic failure. Moreover, the height of the pads may vary with position in order to further reduce fly stiction and dwell stiction, and the locations and/or spacings of the pads may be randomized. For example, pads located near the leading edge of the slider can have a greater height than pads located nearer the trailing edge. Other pad designs may compensate for reduced slider-disk separation with sliders having crown portions. Thus, the terms “padded head” or “padded slider” as utilized herein include all head or slider designs utilizing pads formed on the lower, sliding surface thereof for stiction control, regardless of their number, size, shape, location, and spacing.
There exists a need for improved, high bit or areal recording density, smooth-surfaced magnetic hard disk data/information recording, storage, and retrieval media and systems which are capable of use at very low head slider flying heights on the order of about 0.7 μinch or less, such as about 0.5 μinch, which media and systems exhibit low friction, stiction, and good tribological properties for minimizing head crashing. Moreover, there exists a need for improved, high areal recording density, hard disk media and systems which can be manufactured according to conventional methodologies and are fully mechanically compatible with conventional magnetic hard disk systems.
The present invention addresses and solves problems attendant upon the design and manufacture of high areal recording density magnetic hard disk media and systems utilizing head sliders operating at very low glide heights, while maintaining full compatibility with all mechanical aspects of conventional hard disk drive technology. Moreover, manufacture and implementation of the present invention can be obtained at a cost comparable to that of existing technology.